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Hunkeler, Daniel

Nom
Hunkeler, Daniel
Affiliation principale
Fonction
Professeur ordinaire
Email
daniel.hunkeler@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/142

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  • Publication
    Accès libre
    Application of Diagnostic Tools to Evaluate Remediation Performance at Petroleum Hydrocarbon-Impacted Sites
    (2018-9)
    Bouchard, Daniel 
    ;
    Hunkeler, Daniel 
    ;
    Madsen, E.L.
    ;
    Buscheck, Thomas
    ;
    Daniels, E.
    ;
    Kolhatkar, R.
    ;
    De Rito, C. M.
    ;
    Aravena, Ramon
    ;
    Thomson, N.
    In situ treatment technologies for petroleum hydrocarbon-impacted sites (e.g., multiphase extraction, air sparging, soil vapor extraction, or in situ chemical oxidation) usually rely on a specific chemical, microbial, or physical contaminant removal process. However, target contaminant concentrations can also vary due to other co-occurring processes (e.g. delivery of remedial fluids, natural variability), which can confound the ability to demonstrate treatment efficiency. This technical note proposes a methodology that integrates several diagnostic tools to assess treatment performance. Stable isotope methods and biomarkers were selected because they provide process-specific and, often, also compound-specific information on contaminant removal. The isotope tools include compound-specific isotope analysis that can be used to discriminate between a broad range of removal processes, and isotope analysis of oxidants and degradation end products to assess overall transformation of hydrocarbons. The biomarkers cover characteristic metabolites and functional genes on a mRNA rather than DNA level to understand biological activity more carefully. This technical note integrates information from laboratory and field studies, especially controlled-field experiments where the tools have been evaluated side-by-side for different treatment methods. A tiered approach is proposed to deploy the tools in a stepwise manner until sufficient information is obtained to confidently identify the mass removal processes of interest and demonstrate efficacy of the intended treatment mechanism. The order of tool application considers the type of information that can be gained, the level of certainty, and the ease of implementation. The objective of this technical note is to enable widespread use of these diagnostic tools with the motivation to improve the efficacy of in situ treatment systems. © 2018, National Ground Water Association
  • Publication
    Accès libre
    Infiltration of Sulfate to Enhance Sulfate-Reducing Biodegradation of Petroleum Hydrocarbons
    (2018-9)
    Wei, Yunxiao
    ;
    Thomson, Neil R.
    ;
    Aravena, Ramon
    ;
    Marchesi, Massimo
    ;
    Barker, James F.
    ;
    Madsen, Eugen L.
    ;
    Kolhatkar, Ravi
    ;
    Buscheck, Timothy E.
    ;
    Hunkeler, Daniel 
    ;
    deRito, Christopher M.
    The lack of sufficient electron acceptors, particularly sulfate, can limit the rate of biodegradation of petroleum hydrocarbons (PHCs). Hence, there is a growing interest by remediation practitioners to deliver sulfate to a PHC impacted saturated zone to enhance biodegradation. When shallow contamination is present in a relatively permeable aquifer and site constraints allow, a cost‐effective approach is to apply sulfate on the ground surface. In this investigation a pilot‐scale experiment was conducted to increase our understanding of the delivery of sulfate using a surface‐based method and the resulting impact on a shallow PHC contaminated aquifer. A surficial infiltration pond positioned on the ground surface above a well‐characterized residual PHC source zone was used to control sulfate dosing. A high‐resolution network near the infiltration pond and downgradient of the source zone was employed to monitor relevant geochemical indicators and PHC concentrations. Compound‐specific isotope analysis (CSIA) was used to identify biodegradation patterns and to investigate the occurrence of microbial sulfate reduction. Selected metabolites and reverse‐transcriptase quantitative polymerase chain reaction analyses of expressed biodegradation genes (as mRNA) were also used to characterize the response of indigenous microorganisms (especially sulfate‐reducing bacteria) to the added sulfate. Three sulfate application episodes (5000 L each) at various Na2SO4 concentrations were allowed to infiltrate under a constant hydraulic head. Although the applied sulfate solution was impacted by density‐driven advection, detailed monitoring data indicated that the sulfate‐enriched water mixed with upgradient groundwater as it migrated downward through the residual PHC zone and formed a co‐mingled downgradient plume with the dissolved PHC compounds. The enrichment of δ34S of sulfate in conjunction with a decrease in sulfate concentration showed the occurrence of sulfate reduction due to the applied sulfate. Increased dissolved inorganic carbon (DIC) concentrations associated with a shift toward more depleted values of δ13C of DIC was indicative of an input of isotopically depleted DIC from biodegradation of PHCs. Despite fluctuations in benzene, toluene, and o‐xylene (BTX) concentrations, the CSIA data for BTX showed that these compounds were biodegraded. The biomarker data provided supporting evidence that toluene and o‐xylene were undergoing anaerobic biodegradation due to sulfate reduction. This study provides insight into factors controlling surface‐based delivery of sulfate to shallow PHC impacted groundwater systems, and the value of isotopic and molecular‐biological procedures to augment conventional monitoring tools.
  • Publication
    Accès libre
    Diagnostic Tools to Assess Mass Removal Processes During Pulsed Air Sparging of a Petroleum Hydrocarbon Source Zone
    (2018-6)
    Bouchard, Daniel 
    ;
    Marchesi, Massimo
    ;
    Madsen, Eugen L.
    ;
    DeRito, Christoph
    ;
    Thomson, Neil R.
    ;
    Aravena, Ramon
    ;
    Barker, Jim
    ;
    Buscheck, Thomas
    ;
    Kolhatkar, Ravi
    ;
    Daniels, Eric J.
    ;
    Hunkeler, Daniel 
    During remediation of contaminated aquifers, diagnostic tools can help evaluate whether an intended mass removal process was successfully initiated and acted on specific contaminants of concern. In this study, several diagnostic tools were tested in a controlled‐release in situ air sparging experiment that focused on the treatment of target hydrocarbons (e.g., benzene, toluene, ethylbenzene, and xylenes). The tools included compound‐specific isotope analysis (CSIA), expression of functional genes (mRNA), and metabolites characteristic of aerobic and anaerobic biodegradation. Total and compound‐specific mass balances were established and used, along with traditional monitoring parameters, to validate the results from the various tools. CSIA results indicated biodegradation as the main process contributing to benzene and toluene removal. Removal process‐specific isotope shifts were detected in groundwater as well as in the system effluent gas. CSIA, metabolite, and mRNA biomarkers consistently indicated that both aerobic and anaerobic biodegradation of benzene and toluene occurred, but that their relative importance evolved over time and were related to the treatment system operation. While the indicators do not allow quantification of the mass removed, they are particularly useful to identify if a removal process has been initiated, and to track relative changes in the predominance of in situ contaminant attenuation processes resulting from remediation efforts.
  • Publication
    Accès libre
    Hydrogen Isotope Fractionation during the Biodegradation of 1,2-
    (2017-8)
    Shouakar-Stash, Orfan
    ;
    Hatijah Mortan, Siti
    ;
    Yu, Rong
    ;
    Rosell, Monica
    ;
    Marco-Urrea, Ernesto
    ;
    Freedman, David L.
    ;
    Aravena, Ramon
    ;
    Soler, Albert
    ;
    Hunkeler, Daniel 
    Even though multi-element isotope fractionation patterns provide crucial information with which to identify contaminant degradation pathways in the field, those involving hydrogen are still lacking for many halogenated groundwater contaminants and degradation pathways. This study investigates for the first time hydrogen isotope fractionation during both aerobic and anaerobic biodegradation of 1,2-dichloroethane (1,2-DCA) using five microbial cultures. Transformation-associated isotope fractionation values (εbulk H ) were −115 ± 18‰(aerobic C−H bond oxidation), −34 ± 4‰ and −38 ± 4‰ (aerobic C−Cl bond cleavage via hydrolytic dehalogenation), and −57 ± 3‰and −77 ± 9‰ (anaerobic C−Cl bond cleavage via reductive dihaloelimination). The dual-element C−H isotope approach (ΛC−H = Δδ2H/Δδ13C ≈ εbulk H /εbulk C , where Δδ2H and Δδ13C are changes in isotope ratios during degradation) resulted in clearly different ΛC−H values: 28 ± 4 (oxidation), 0.7 ± 0.1 and 0.9 ± 0.1 (hydrolytic dehalogenation), and 1.76 ± 0.05 and 3.5 ± 0.1 (dihaloelimination). This result highlights the potential of this approach to identify 1,2-DCA degradation pathways in the field. In addition, distinct trends were also observed in a multi- (i.e., Δδ2H versus Δδ37Cl versus Δδ13C) isotope plot, which opens further possibilities for pathway identification in future field studies. This is crucial information to understand the mechanisms controlling natural attenuation of 1,2-DCA and to design appropriate strategies to enhance biodegradation.
  • Publication
    Accès libre
    Does sorption influence isotope ratios of chlorinated hydrocarbons under field conditions
    (2017-7)
    Wanner, Philip 
    ;
    Parker, Beth L.
    ;
    Chapman, Steven W.
    ;
    Aravena, Ramon
    ;
    Hunkeler, Daniel 
    This study aims to investigate the effect of sorption on isotope ratios of chlorinated hydrocarbons migrating through the subsurface. For this purpose concentration and isotope ratio profiles (carbon and chlorine) were determined in saturated low permeability sediments below two DNAPL sources (1,2- Dichloroethane (1,2-DCA) and Dichloromethane (DCM)). The sources had been emplaced artificially as part of a long-term, emplaced source field experiment 15.5 years (5673 days) ago. Low permeable sediments are well-suited for investigating sorption-induced isotope fractionation under field conditions. The advancing concentration front, where isotope fractionation due to sorption is expected, can be localized precisely and sampled at a high spatial resolution. Along a concentration profile below the 1,2- DCA and DCM DNAPL sources, opposite isotope trends were observed with an enrichment of heavy carbon isotopes (Dd13C ¼ 1.9‰for 1,2-DCA and 2.4‰for DCM) and a depletion of heavy chlorine isotopes (Dd37Cl ¼ 1.3‰ for 1,2-DCA). For field data interpretation laboratory experiments were conducted to determine sorption and diffusion-induced isotope fractionation factors for 1,2-DCA and DCM and included in a numerical model. When considering only diffusive isotope fractionation, numerical simulation failed to reproduce the opposite isotope trends. In contrast when sorption-induced isotope fractionation was also included, the model reproduced the data well. Hence, the observed isotope trends reflect a superposition between competing isotope effects due to sorption and diffusion. For chlorine the diffusive isotope effect is larger than for carbon due to the mass difference of two between the stable isotopes overruling the sorption effect, while for carbon the sorption effect dominates. The observed shifts of isotope ratios due to sorption are in the range of the 2‰ threshold value, which is often used for identifying reactive processes. Numerical modelling showed that under specific conditions (strong sorption behavior, early transient diffusion) even higher shifts of isotope ratios can occur. Hence, when shifts of isotope ratios in the range of 2‰ are observed under field conditions where sorption prevails, their attribution to reactive processes should be made with caution. This is especially crucial if a reactive process is slow and associated with a small isotope fractionation factor.
  • Publication
    Accès libre
    Quantification of Degradation of Chlorinated Hydrocarbons in Saturated Low Permeability Sediments Using Compound-Specific Isotope Analysis
    (2016-5)
    Parker, Beth L.
    ;
    Chapman, Steven W.
    ;
    Aravena, Ramon
    ;
    Hunkeler, Daniel 
    This field and modeling study aims to reveal if degradation of chlorinated hydrocarbons in low permeability sediments can be quantified using compound-specific isotope analysis (CSIA). For that purpose, the well-characterized Borden research site was selected, where an aquifer−aquitard system was artificially contaminated by a three component chlorinated solvent mixture (tetrachloroethene (PCE) 45 vol %, trichloroethene (TCE) 45 vol %, and chloroform (TCM) 10 vol %). Nearly 15 years after the contaminant release, several highresolution concentration and CSIA profiles were determined for the chlorinated hydrocarbons that had diffused into the clayey aquitard. The CSIA profiles showed large shifts of carbon isotope ratios with depth (up to 24‰) suggesting that degradation occurs in the aquitard despite the small pore sizes. Simulated scenarios without or with uniform degradation failed to reproduce the isotope data, while a scenario with decreasing degradation with depth fit the data well. This suggests that nutrients had diffused into the aquitard favoring stronger degradation close to the aquifer−aquitard interface than with increasing depth. Moreover, the different simulation scenarios showed that CSIA profiles are more sensitive to different degradation conditions compared to concentration profiles highlighting the power of CSIA to constrain degradation activities in aquitards.
  • Publication
    Accès libre
    Evaluating the fate of chlorinated ethenes in streambed sediments by combining stable isotope, geochemical and microbial methods
    (2009)
    Abe, Yumiko
    ;
    Aravena, Ramon
    ;
    Zopfi, Jakob 
    ;
    Parker, Beth
    ;
    Hunkeler, Daniel 
    The occurrence of chlorinated ethene transformation in a streambed was investigated using concentration and carbon isotope data from water samples taken at different locations and depths within a 15×25 ms tudy area across which a tetrachloroethene (PCE) plume discharges. Furthermore, it was evaluated how the degree of transformation is related to groundwater discharge rates, redox conditions, solid organic matter content (SOM) and microbial factors. Groundwater discharge rates were quantified based on streambed temperatures, and redox conditions using concentrations of dissolved redox-sensitive species. The degree of chlorinated ethene transformation was highly variable in space from no transformation to transformation beyond ethene. Complete reductive dechlorination to ethane and ethene occurred at locations with at least sulfate-reducing conditions and with a residence time in the samples streambed zone (80 cm depth) of at least 10 days. Among these locations, Dehalococcoides was detected using a PCR method where SOM contents were >2% w/w and where transformation proceeded beyond ethene. However, it was not detected at locations with low SOM, which may cause an insufficient H2 supply to sustain a detectably dense Dehalococcoides population. Additionally, it is possible that other organisms are responsible for the biodegradation. A microcosm study with streambed sediments demonstrated the potential of VC oxidation throughout the site even at locations without a pre-exposure to VC, consistent with the detection of the epoxyalkane:coenzyme M transferase (EaCoMT) gene involved in the degradation of chlorinated ethenes via epoxidation. In contrast, no aerobic transformation of cDCE in microcosms over a period of 1.5 years was observed. In summary, the study demonstrated that carbon isotope analysis is a sensitive tool to identify the degree of chlorinated ethene transformation even in hydrologically and geochemically complex streambed systems. In addition, it was observed that the degree of transformation is related to redox conditions, which in turn depend on groundwater discharge rates.
  • Publication
    Accès libre
    Carbon and chlorine isotope fractionation during aerobic oxidation and reductive dechlorination of vinyl chloride and cis-1,2-dichloroethene
    (2009)
    Abe, Yumiko
    ;
    Aravena, Ramon
    ;
    Zopfi, Jakob 
    ;
    Shouakar-Stash, O
    ;
    Cox, E
    ;
    Roberts, J.D
    ;
    Hunkeler, Daniel 
    The study investigated carbon and chlorine isotope fractionation during aerobic oxidation and reductive dechlorination of vinyl chloride (VC) and cis-1,2-dichloroethene (cDCE). The experimental data followed a Rayleigh trend. For aerobic oxidation, the average carbon isotope enrichment factors were -7.2‰ and-8.5‰ for VC and cDCE, respectively, while average chlorine isotope enrichment factors were only -0.3‰ for both compounds. These values are consistent with an initial transformation by epoxidation for which a significant primary carbon isotope effect and only a small secondary chlorine isotope effect is expected. For reductive dechlorination, larger carbon isotope enrichment factors of -25.2‰ for VC and -18.5‰ for cDCE were observed consistent with previous studies. Although the average chlorine isotope enrichment factors were larger than those of aerobic oxidation (-1.8‰ for VC, -1.5‰ for cDCE), they were not as large as typically expected for a primary chlorine isotope effect suggesting that no cleavage of C-Cl bonds takes place during the initial ratelimiting step. The ratio of isotope enrichment factors for chlorine and carbon were substantially different for the two reaction mechanisms suggesting that the reaction mechanisms can be differentiated at the field scale using a dual isotope approach.
  • Publication
    Accès libre
    Carbon Isotope Fractionation during Diffusion and Biodegradation of Petroleum Hydrocarbons in the Unsaturated Zone: Field Experiment at Værløse Airbase, Denmark, and Modeling
    (2008)
    Bouchard, Daniel 
    ;
    Hunkeler, Daniel 
    ;
    Gaganis, Petros
    ;
    Aravena, Ramon
    ;
    Höhener, Patrick
    ;
    Broholm, Mette M.
    A field experiment was conducted in Denmark in order to evaluate the fate of 13 volatile organic compounds (VOCs) that were buried as an artificial fuel source in the unsaturated zone. Compound-specific isotope analysis showed distinct phases in the 13C/12C ratio evolution in VOC vapors within 3 m from the source over 114 days. At day 3 and to a lesser extent at day 6, the compounds were depleted in 13C by up to −5.7‰ with increasing distance from the source compared to the initial source values. This trend can be explained by faster outward diffusion of the molecules with 12C only compared to molecules with a 13C. Then, the isotope profile leveled out, and several compounds started to become enriched in 13C by up to 9.5‰ with increasing distance from the source, due to preferential removal of the molecules with 12C only, through biodegradation. Finally, as the amount of a compound diminished in the source, a 13C enrichment was also observed close to the source. The magnitude of isotope fractionation tended to be larger the smaller the mass of the molecule was. This study demonstrates that, in the unsaturated zone, carbon isotope ratios of hydrocarbons are affected by gas-phase diffusion in addition to biodegradation, which was confirmed using a numerical model. Gas-phase diffusion led to shifts in δ13C >1‰ during the initial days after the spill, and again during the final stages of source volatilization after >75% of a compound had been removed. In between, diffusion has less of an effect, and thus isotope data can be used as an indicator for hydrocarbon biodegradation.
  • Publication
    Accès libre
    Groundwater–surface water interaction and its role on TCE groundwater plume attenuation
    (2007)
    Chapman, Steven W.
    ;
    Parker, Beth L.
    ;
    Cherry, John A.
    ;
    Aravena, Ramon
    ;
    Hunkeler, Daniel 
    A field investigation of a TCE plume in a surficial sand aquifer shows that groundwater–surface water interactions strongly influence apparent plume attenuation. At the site, a former industrial facility in Connecticut, depth-discrete monitoring along three cross-sections (transects) perpendicular to groundwater flow shows a persistent VOC plume extending 700 m from the DNAPL source zone to a mid-size river. Maximum TCE concentrations along a transect 280 m from the source were in the 1000s of μg/L with minimal degradation products. Beyond this, the land surface drops abruptly to a lower terrace where a shallow pond and small streams occur. Two transects along the lower terrace, one midway between the facility and river just downgradient of the pond and one along the edge of the river, give the appearance that the plume has strongly attenuated. At the river, maximum TCE concentrations in the 10s of μg/L and similar levels of its degradation product cis-DCE show direct plume discharge from groundwater to the river is negligible. Although degradation plays a role in the strong plume attenuation, the major attenuation factor is partial groundwater plume discharge to surface water (i.e. the pond and small streams), where some mass loss occurs via water–air exchange. Groundwater and stream mass discharge estimates show that more than half of the plume mass discharge crossing the first transect, before surface water interactions occur, reaches the river directly via streamflow, although river concentrations were below detection due to dilution. This study shows that groundwater and surface water concentration measurements together provide greater confidence in identifying and quantifying natural attenuation processes at this site, rather than groundwater measurements alone.